1. Field of the Invention
The present invention relates to a mobile communication system, a base station, a mobile station, and a cell control method.
2. Related Background Art
In a mobile communication system, a plurality of base stations establish cells by broadcasting their respective cell selection reference signals. There are also cases where each base station broadcasts directional cell selection reference signals in multiple directions to establish multiple sector cells (such sector cells will also be referred to as “cells” in the present specification).
The size of each cell is determined by a transmitted power of a cell selection reference signal from a base station. Namely, the size of each cell is defined by the size of an area in which the cell selection reference signal reaches at a predetermined power value. A mobile station establishes a connection for communication with a base station from which it can receive the cell selection reference signal at maximum intensity.
When a new base station is added in such a mobile communication system, a neighboring base station notifies the new base station of a transmitted power value of the cell selection reference signal broadcast thereby. The new base station also measures a received power value of the cell selection reference signal transmitted from the neighboring base station. The new base station calculates a propagation loss of the cell selection reference signal from the neighboring base station, using the transmitted power value notified of by the neighboring base station, and the received power value measured. The new base station estimates the cell boundary of the neighboring base station from the calculated propagation loss and controls the transmitted power value of the cell selection reference signal broadcasted by itself, according to the estimated cell boundary. This permits the new base station to autonomously adjust the size of the cell established by itself (for example, reference is made to Hideki Fujibe et al., “Proposal on autonomous cell formation based on arrangement of base stations,” The 2002 IEICE General Conference, B-5-70, Mar. 2002, p520).